The present invention relates to a control apparatus and a control method for a motor drive vehicle in which a motor is employed as a power source.
Motor drive vehicles have been proposed as useful transportation means capable of substituting for an automobile with an internal combustion engine functioning as a power source, namely as a non-pollutional vehicle capable of meeting a requirement for a global world-wide environment protection.
In accordance with the very recent technology, a maximum speed and also an acceleration performance of such a motor drive vehicle closely resemble those of the normal gasoline motorcar. There are two typical motor drive vehicles, namely, one vehicle equipped with a solar cell functioning as a power source thereof and the other vehicle equipped with battery as this power source.
A motor drive vehicle has such superior merits that neither automotive exhaust gas, nor carbon dioxide is emitted and, however, has such problems that a drivable distance achieved by a single or 1-recharging operation of a battery is still shorter than that of a gasoline motorcar up to now. To extend the drive distance achieved by the 1-recharging operation of the battery, energy density of this battery must be increased as well as the efficiencies of the constructive elements of the drive apparatus employed in the motor drive vehicle must be also increased.
With the very recent technology, a driving apparatus system employed in a motor drive vehicle is arranged by a battery, an inverter, a motor, a transmission and a wheel. As the inverter, a bridge type PWM (pulse width modulation) inverter constructed of a highspeed switching element (IGBT power transistor) is utilized. As the motor, either an induction motor vectorcontrolled by such a bridge type PWM inverter, or a synchronous motor with employment of a permanent magnet is used. Further, either a transmission system with three or more stages, or fixed gear ratios is employed.
Since a motor drive vehicle is driven under various road conditions and running conditions, the vehicle must run throughout the wide load range. Accordingly, there are many possibilities that a single motor can not cover such wide load range. Thus, a transmission system is normally utilized, the same as in an internal combustion engine. A motor drive vehicle equipped with a transmission system is known from, for instance, Japanese publications of JP-A-3-128789 and JU-A-3-91001.
The first publication of JP-A-3-128789 filed on Jun. 20, 1990 in Japan discloses the motorcycle with the motor as the power source. This motorcycle employs the automatic centrifugal clutch and is operated in such a manner that when the rotational speed of the motor has reached a certain speed range, either the clutch or the automatic transmission system is automatically coupled with the motor output and the drive shaft.
On the other hand, in JU-A-3-91001 filed on Dec. 27, 1989 in Japan, there is described the drive control apparatus for the motor drive vehicle in which when the motor current reaches a preset limit value, the transmission ratio of the no-stage transmission system is varied.
Furthermore, two Japanese patent publications under numbers of JP-A-58-160661 (filed on Mar. 17, 1982) and JP-A-59-226747 (filed on Jun. 3, 1983) have been opened, although these patents relate not to the motor drive vehicle, but to the gasoline engine automobile equipped with CVT ( continuously variable transmission). More specifically, these patent applications disclose the control apparatus used in such a gasoline engine automobile with the CVT, in which the transmission ratio of the CVT is controlled while driving the gasoline engine at the minimum fuel consumption ratio.